In an area with radioactive risks, it is sometimes necessary to seek and locate the radioactive sources. An attempt is then made to prepare a "map" of the gamma activity of the zone to be monitored by attempting to operate remotely and consequently reducing the risks of contamination for operators.
At present, an apparatus for the remote localization of gamma emitting radioactive sources comprises a gamma ray detector, a distance sensor and a video camera. This apparatus travels on rails and can be moved in accordance with limited angles towards the sources to be located. A converter converts the signals transmitted by the gamma ray detector and distance sensor into colored zones on a control screen. A first image showing the intensity and distribution of the gamma rays emitted by the radioactive sources is therefore formed point-by-point. On said first image is superimposed a second image from the video camera, in order to permit the location of the sources as a function of their intensity in the zone to be monitored.
Such an apparatus is difficult to transport and realize as a result if its weight, complexity and fragile nature, so that the detector and camera have to be manipulated carefully. It is therefore not very suitable for use as an apparatus for monitoring nuclear installations, where radioactive sources can appear at random locations. The time for obtaining the first image is very long and it is consequently difficult to rapidly obtain several photographs. As a result of its complexity, the apparatus is very costly, which makes it impossible to install such an apparatus permanently in each zone to be monitored.
U.S. Pat. No. 3,107,276 describes an apparatus for the localization of radioactive sources designed to be airborne and having a pinhole camera made from a shielding material. This camera is provided with a scintillation converter associated with a cathode ray tube, which converts the image focused by the pinhole into electronic signals with a view to their teletransmission. An independent video camera makes it possible to display the space to be monitored. In such an apparatus, the superimposing of the video image and the image of the radioactive sources is very difficult to bring about on an accurate basis. Moreover, the apparatus has large dimensions, is costly to manufacture and use and is not very suitable for use within a building.